Method of incorporating water soluble epoxypropyl starch into paper

ABSTRACT

A PROCESS IS DISCLOSED FOR PREPARING PAPER HAVING INCORPORATED THEREIN AN EPOXYPROPYL STARCH. AT EPOXYPROPYL D.S. OF UP TO .09 THE COMPOUNDS ARE WATER SOLUBLE AND INCREASE BOTH WET AND DRY STRENGTH OF PAPER AT A 1-PERCENT LEVEL OF ADDITION.

United States Patent O M 3,834,984 METHOD OF INCORPORATING WATER SOLUBLEEPOXYPROPYL STARCH INTO PAPER Robert E. Wing, Peoria, and William M.Doane, Morton,

Ill., assignors to the United States of America as represented by theSecretary of Agriculture No Drawing. Original application Dec. 21, 1971,Ser. No. 210,549, now Patent No. 3,795,671. Divided and this applicationAug. 9, 1973, Ser. No. 386,921

Int. Cl. D211 3/28 US. Cl. 162-175 2 Claims ABSTRACT OF THE DISCLOSURE Aprocess is disclosed for preparing paper having incorporated therein anepoxypropyl starch. At epoxypropyl D.S. of up to .09 the compounds arewater soluble and increase both wet and dry strength of paper at al-percent level of addition.

.This is a division of application Ser. No. 210,549, filed Dec. 21,1971, now US. Pat. 3,795,671.

A nonexclusive, irrevocable, royalty-free license in the inventionherein described, throughout the world for all purposes of the UnitedStates Government, with the power to grant sublicenses for suchpurposes, is hereby granted to the Governmentof the United States ofAmerica.

BACKGROUND OF THE INVENTION This invention relates to the preparation ofstarch derivatives and more specifically to starch derivativescontaining pendant alkyl epoxides. The invention also relates to the useof epoxypropyl starches as paper additives which increase wet and drystrength.

Most alkyl epoxide-containing carbohydrates recorded in the literaturehave been prepared by reacting monoand oligosaccharides withepichlorohydrin in the presence of a Lewis acid, with hypochlorous acidto first form chlorohydrins followed by dehydrochlorination with sodiumhydroxide, or with allyl halides to first form allyl ether derivativeswhich are then oxidized with a peracid. This last method has been usedto attach alkyl epoxides to a variety of monosaccharides, US. 3,414,560;E. W. Thomas, Carbohyd. Res. 13: 225-228 (1970); and R. E. Wing et al.,Carbohyd. Res. 12: 285-289 (1970'). However, no epoxides were formed byattempts to attach alkyl epoxy groups to the free hydroxyls on theglucose units of starch by reacting allyl starch with peracetic acid[Inano, Chem. Soc. Japan, Inc. Chem.-Sect. (Kogyo Kagaku Zasshi), Vol.70, 9, 1550-1553 (1967)] or with a benzonitrile-SO percent hydrogenperoxide solution. Inano was able to achieve a reaction between sodiumcarboxymethyl starch and epichlorohydrin from which he obtained awater-insoluble product containing 1.4 mole percent carboxymethylepoxypropyl groups.

The direct reaction of starch with epichlorohydrin in an aqueousalkaline solution is a commercial process which forms inhibited (i.e.,crosslinked) starch products resistant to swelling or gelatinization.These products show marked inhibitionto hot water swelling with as fewas one epoxypropyl group per 1200 anhydroglucose units (AGU) of starchwhich corresponds to an epoxypropyl D.S. of 0.0008 [see B. M. Gough, DieStarke, 8: 240-243 (1967)'for an explanation of the mechanism ofcrosslinks in this reaction].

Inhibited starches being essentially insoluble in water are limited touses such as viscosity-stable pastes and water-resistant adhesives.However, water-soluble starches containing intact epoxide side chainswould be useful in many areas especially as strength-increasingadditives in various paper products.

3,834,984 Patented Sept. 10, 1974 We have discovered a process forproducing epoxypropyl starches which can be either water-soluble or-insoluble depending on reaction conditions. It comprises the followingsteps:

a. reacting sodium hydride (NaH) with a starch or starch derivative,having free hydroxyl groups on the anhydroglucose units, in a dimethylsulfoxide (DMSO) solution;

reacting the products resulting from step (a) with epichlorohydrin toform epoxypropyl starch; and c. recovering the epoxypropyl starch fromthe reaction mixture.

Epoxypropyl starch is defined herein to include the products preparedfrom starch and starch derivatives.

A soluble product is obtained when about 0.18 to about 0.34 mole of NaHis reacted per mole (AGU) of starch or starch derivative. These productswill have an epoxypropyl D.S. of about 0.03 to about 0.09. At reactantratios greater than 0.34, the resulting products are water-insoluble.The general formula of the water-soluble epoxypropyl starch products isas follows:

0 S. O CH. C CH.)

D.S- where St=starch or starch derivative having free hydroxyl groupsand D.S.:the degree of substitution of the epoxypropyl group=0.03 to0.09. The above water-soluble epoxypropyl starches are used in themanufacture of paper. Both the wet and dry strength of paper isincreased when the products are applied at a 1-percent level of additionbased on dry pulp weight.

DETAILED DESCRIPTION OF THE INVENTION The reaction by which alkylepoxides are attached to a starch substrate appears to be as follows:

0 CHZDHCHzCl where St=starch, starches, starch products, or starchderivatives that contain free hydroxyl groups react in accordance withthe claimed process to produce epoxypropyl starch. Examples of starchesare cereal starches (e.g., corn, wheat, rye, sorghum) and root androot-type starches (e.g., tapioca, potato, waxy maize, waxy sorghum).Examples of starch products are cereal grain flour, grits, and flakes.Examples of starch derivatives are cationic starch [e.g.,N-(Z-hydroxypropyl)-diethylamino starch, tertiary or quaternary ammoniumstarch, quaternary phosphonium starch, tertiary sulphonium starch, andaminoethyl starch]; starch ethers (e.g., methyl starch, hydroxyethylstarch, allyl starch, carboxymethyl starch, and Z-cyanoethyl starch);starch esters (e.g., starch acetate, starch sulfonates, starch sulfate,and starch phosphate); oxidized starch; and starch graft copolymers.

It is understood that examples of starch, starch products, and starchderivatives other than those specifically stated above which react inaccordance to the claimed process will be known to those skilled in theart, and that the invention should not be limited to those examplesdescribed above.

The solvent in which the reaction takes place should be nonaqueous andone in which starch is at least partially soluble. Water should beexcluded as much as possible in order to minimize its reaction with NaH.Starch is soluble in DMSO making it the preferred solvent. However, thereaction can be conducted in dimethylformamide and tetrahydrofuran. V

In the first step of the process the starch starting material dissolvedin DMSO will theoretically react stoichio- Moisture of pearl starch.percent Temperature of reaction mixture when NaH added, C 60.4...

metrically with NaH depending on the number of free hydroxyl groupsavailable. The preferred ratio of NaI-I to starting material is from 0.2to 0.7 mole of NaH per AGU of starch or starch derivative which, aftersubsequent reaction with epichlorohydrin, gave final products havingepoxypropyl -D.S. levels of from 0.03 to 0.14. In order to produce afinal product which is water-soluble, the ratio of reactants should bein the range of 0.18 to 0.34 mole NaH per AGU and the final epoxypropylstarch product should have a D5. of from 0.03 to 0.09. This first stepreaction should be conducted within a temperature range of from 6 C. to100 C. These are the melting and decomposition temperatures of DMSO. Atthe preferred temperatures of from 25 C. to 60 C. the reaction will becomplete within about one-half hour. However, reactions were usuallyallowed to proceed for up to 3 hours. The product of the reactionsbetween NaH and starch or starch derivatives will herein be calledsodium-starch.

Although epichlorohydrin will essentially react stoichiometn'cally withsodium-starch, it is preferred that excess epichlorohydrin be used toinsure complete reaction. This second step reaction should be conductedat temperatures below 100 C. to minimize evaporation of epichlorohydrinand because DMSO is still present. The reaction was allowed to proceedfor as little as 1 hour and as long as 18 hours at a preferredtemperature range of between 25 C. to 90 C. Neither temperature norreaction time appears to be critical.

The third and final step in the process for producing epoxypropyl starchis product recovery, which can be performed in several ways such assolvent extraction. The easiest, most convenient, and preferred methodis based on the products insolubility in alcohol. After alcoholprecipitation, the epoxypropyl starch is filtered, washed, and dried.

Water-soluble epoxypropyl starches prepared according to the inventionhaving D.S. levels of from 0.03 to 0.09 were tested for their ability toincrease paper strength using TAPPI Standard Method T 205 111-58,Forming Handsheets for Physical Tests of Pulps, T 404 ts-66, TensileBreaking Strength of Paper and Paperboard, and T 456 os-68, Wet TensileBreaking Strength of Paper and Paperboard. Because of their completewater solubility and their lack of functional groups, epoxypropylstarches prepared from untreated gelatinized pearl corn starch were notsufficiently retained by the cellulose fibers to produce any significantincreases in paper strength when added to pulp furnishes prior topreparing handsheets. Therefore, aqueous solutions of these productswere sprayed onto wet paper mats prior to the final drying step at al-percent level of addition (based on dry fiber weight). The mats, withor without a subsequent acidic or basic treatment to cause oxirane ringopening, were heated at 75 C. for 1 hour before conditioning.improvements were observed in wet breaking length of two to nine timesand in dry breaking length of up to 20 percent over the untreatedcontrols.

The larger increases in wet-tensile strength were realized Weight ofether-washed NaH g 0. 485 I TABLE 1 when the mats were treated withsolutions of polyethylenimine, sodium carbonate, sodium bicarbonate, oracetic acid to effect ring opening. Increase in dry-tensile strength waslarger when the mats were not treated with these solutions. The surfaceapplication of pearl corn starch to mats with the same subsequenttreatments showed some increase indry breaking length .over'the controlsbut no significant increase. in wet breaking length. 1.

To illustrate the use of starch derivatives as strengthincreasing paperadditives, acommercial cationicstarcli was treated by the DMSO-sodiumhydride-epichlorohydrin system under various conditions which aliordedepoxypropyl starches Witha'range' of epoxypropyl D5.

of 0048-0076. Being cationic these products are sufficiently retained bycellulose fibers so that wet-end addition (i.e., addition to'pulp'furnish) can-be used.

Handsheets were made containing an epoxypropylated (D.S. 0.064) cationicstarch that had been addedat a l-percent level to a pulp furnish of pH7.0. For cornparison, handsheets were made containing a commercialcationic starch added under identical conditions, Handsheets preparedwith the epoxypropyl starch increased in dry-tensile strength 27 percentand wet-tensile strength 200 percent over handsheets made with acommercial cationic starch. With furnish adjusted to pH 5.5, drytensilestrength did not improve, but wet-tensile strength increased 350percent. Results weresimilar with"D.S. 0.048 and 0.076 epoxypropylcationic starches. Addition levels of 0.25 and 0.50 percent gave smallerincreases in Wet tensile. When 10 percent clay was added 'to' thefurnish at pH 5.5, the addition of the cationic epoxypropyl derivativeresulted in a 120-percent increase in wet-tensile and a 34-percentincrease in ash content as compared with a commercial cationicstarchpVari'ous treatments of the handsheets after the second TAPPIpress to promote further opening of the oxirane'ring failed to show anyadditional strength increase-Evaluation of these products as spray-onadditives by procedures reported for epoxypropyl starch revealed maximumincreases of 35 and 220 percent in dryand wet-tensile strength,respectively, when compared to the commercial cationic starch.

The following examples are intended to further illustrate but not limitthe invention as claimed.

EXAMPLES 1- 1. Untreated gelatinized pearl corn starch (10 g 13 percentmoisture) was stirred in DMSO (200 ml.) for 3 hours at C., and thensodium hydride .was added. After an additional 3 hours of stirring thereaction mixture was cooled to 25 C., epichlorohydrin (20 ml.) wasadded, and the mixture was stirred for 4 hours at C. The mixture wascooled and'poured into ethanol (2 liters). The solid was removed byfiltration; washed with ethanol (1 liter), acetone (0.5 liter), andhexane (05 liter); and dried in a vacuum oven at 60 C.; yield 9.05 g.,003-118. In other examples one or more variable in the reaction wereintroduced (Table 1). r

NaH added as.-- Solid sliglrgsii Sl1]1)r1i;y i3 Slurry in Slurry in- 18DMSO. DM' Temperature of nurture when epiehlorohydrin added, 0-; 25 25 525 60 SO 25P Temperature and time of reaction, C.'-hours 90- 90- 90225-18, 90-1. 60-1; 25-18, 90-1 ,-Weight of product, g. p 9. 05 8. 89 10.56 9. R1 O. 11. 13. Chlorlne, per fl ,0. 49 0. 0. 0. 61.; 0.78 3. 96.

D.S. 0. 03;. 0.05 0.07 0.09 a 105' *0. 14; Solubility in water pSoluble- Soluble. Soluble Soluble Mostly I Mostly insoluble.

111 each example 10.0 g. pearl corn starch was used. NeH=sodium by e. v

8 DMSO =dimethyl sulioxide.

d Determined by pyridine hydroehloridemethod of Inano, supra.

Derivative (1.5 g.) in ml. water at 90 C. for 1 hour; then 0001. i

insoluble.

. 6 placed in an oven at 75 C. for 1 hour. After drying they were thenconditioned and-tested for wet anddry breaking length by TAPPI StandardMethods, supra (Table 3). The basis weight of handsheets was 60 g./m.

TABLE 3 Physical testing (breaking length, m.) of handsheets treatedwith epoxypropyl starch Epoxypropyl starch (D.S.)

a 0.00 0. 03 0, 05 0. 07 0. 09 Control Treatment 5 Dry Wet Dry Wet DryWet Dry Wet Dry Wet Dry Wet None 6 7, 940 155 7, 283 250 8, 294 560 8,152 495 7, 734 550 6, 879 100 Water 7, 100 125 6, 904 235 7, 772 555 8,019 425 7, 437 395 5, 892 130 4% N020 03 6, 440 150 6, 295 305 7, 170870 7, 448 555 7, 300 640 5, 567 150 140 6, 278 270 7, 138 690 7, 107560 7, 238 725 4, 796 135 PEI-6 200 6, 566 355 7, 557 900 7, 713 815 7,162 805 5, 882 180 4% CHQCO OH 165 6, 381 240 7, 995 730 7, 820 505 6,984 700 5, 457 120 8 Added to about 1 g. wet pickup. b About a l-percentaddition. Untreated gelatinized pearl corn starch.

2 hours at 80 C., cooled to 25 C., and sodium hydride (0.165 g.) addedasslurry in DMSO (50 ml.). After an additional 4 hours of stirring,epichlorohydrin ml.) was added and the mixturewas stirred for 18 hoursat C., then 1 hour at 80 C. The mixture was cooled and poured intoethanol (2 liters). The solid was removed by filtration, washed withethanol (1 liter), acetone (0.5 liter), and hexane (0.5 liter), anddried in a vacuum oven at 60 0.; yield 9.4 g. An oXirane analysisconducted In each example 10.0 g. cationic starch was used. Temperatureand time of reaction C.-hour); 25-18 then 80-1.

b NaH=sodium hydride.

* Cationic starch=0.78 percent chlorine.

d Determined by pyridine hydrochloride method of Inano, supra.

EXAMPLE 11 Unbleached kraft pulp was refined in a 5-1b. Valley heater toa freeness of 590 ml. CSF. Wet paper mats were prepared at pH 7 in aBritish sheet machine, pressed according to TAPPI Standard Methods, andused without further drying. At this point solutions of the epoxypropylstarch products from Examples l-4 were prepared by placing 1.5 g. ofeach product in 100 ml. of water and stirring at 90 C. for 1 hour. Eachsolution was cooled and applied to the wet paper mats by spraying with abottle sprayer under constant air pressure to a level of about 1 percentstarch based on the dry Weight of the cellulose fibers. The mats wereallowed to air-dry for 15 min. and then were again sprayed with thevarious acidic and basic solutions to a 1 g. wet pickup (Table 3). Themats were mounted in TAPPI standard rings and d No chemicalsprayapplied. 6 Polyethylenlmine-molecular weight, 600 (Dow Chemical 00.).

EXAMPLE 12 Unbleached softwood sulfate pulp [15 g., oven-dry (0.d.)basis] was slurried in a British Disintegrator at 1 percent consistencyand diluted to 6150 g. with tap water. With continuous mixing, theadditives (0.15 g./100 ml. water) were added to the pulp slurry and thepH was adjusted with 10 percent sulfuric acid. Handsheets g./m. weremade with no further pH adjustment in the sheet mold. After pressing,some of the sheets were oven dried, or sprayed with acarbonate-bicarbonate solution, and then the sheets were conditioned andtested according to TAPPI Standard Methods, supra, Table 4. Clay wasused in some tests at a 10 percent level and was added before pHadjustment, Table 5.

TABLE 4 Breaking length, In. of handsgeeltghtreated with epoxypropylcationic Applied as wet-end additive.

b Samples were stirred in water ml.) at 90 C. for 30 minutes beforeadding to furnish at various levels.

D.S. refers to epoxypropyl D.S. of certain eplchlorohydrin-treatedcationic starch samples. I

d Thirty-minute immersion in distilled water for wet tensile.

N-(Z-hydroxypropyl)-diethylarnino starch.

* Product of Example N0. 7.

Product of Example No. 8.

11 Product of Example No. 9.

Product of Example No. 10.

TABLE 5 Breaking Length, m. and Ash Content of Handsheets Treated withEpoxypropyl Cationic Starch and Clay Treatment b Standard 2% NazCOs,TAPPI 1 hour, 10 lmnutes, 2% NaHCO methods 75 0. C. 1 hour, 75 0. Ash,

per- Sample evaluated Dry Wet Dry Wet Dry Wet Dry Wet cent H 7.0: pControl 160 6, 170 6,070 160 5, 780 200 1. 15 1% cationic star 6, 320 6,230 150 5, 500 0.86 1% 0.064 D.S. 170 6, 610 6, 310 5, 440 220 1. 39 H5.5: p Control 165 7, 030 205 6, 730 180 6, 420 220 1. 29 1% cationicstarch d 170 7, 980 205 7,870 200 7, 680 260 1. 69 1% 0.064 D.S. B 7,230 380 7, 390 490 7,720 470 7, 100 585 2. 27

8 Applied as wet-end additive; 10 percent clay. b Various treatmentsafter second TAPPI press. Sprayed on to a 1 g. wet pickup after secondTAPPI press. 6 Samples of N-(Z-hydroxypropyl)-diethylamino starch (0.15g., D.S.) were stirred in water (100 ml.) at

90 C. for 30 minutes.

' D.S. of epoxypropyl cationic starch of Example 10.

j t I EXAMPLE 1 .3 ""The product ofExample" was applied to wet papermats as'deser'ibed in Example 11 and tested for breaking length,Tableifi V TABLE 6 Breaking length, m gi handsheets treated with D.S.0.064 epoxypropy cationic starch as a spray-on additive 0.064 D.S.Cationic epoxypropyl Control I starch cationic starch TreatmentpH 7.0Dry Wet Dry Wet Dry Wet 4% NaHC'Oa 6, 390 230 5, 960 225 7, 430 580 2%N21200:; D1115 2% NaHC 245 5, 640 210 7, 360 645 4% EtaN 180 5, 810 2057, 430 495 4% P Eli-6 300 5, 480 280 7, 360 730 4% OH C O O H 6, 150 2155, 270 185 6, 920 480 Added to about 1 g. wet pickup; then dried 1 hourat 75 C. About 1 percent addition. No chemical spray applied.

d Polyethylenimine-moleeular weight 600 (Dow Chemical 00.).

We claim:

1. In the production of paper an improvement which increases both wetand dry strength comprising the addition of about 1 percent, based ondry pulp weight, of a water-soluble epoxypropyl starch comprising thefollowing structure:

where St is starch or starch derivative having free bydroxyl groups onthe anhydroglucose units and D.S. is

8-. 0.03 to 0.09, the addition heing-, m ade by spraying an aqueoussolution of said epoxypropyl starch onto a wet paper'mat prior'todrying. 2. In theprodu cti on of paper an improvement which increasesboth wet and dry strength comprising the addi- 'tion of from 0.25 to 1percent, based on dry pulp weight,

of a water-soluble epoxypropyl starch comprisingthe following structure:

0 st-oc1no crn) where St is catonic starch having free hydroxyl'groupson the anhydroglucose units and D.S. is-0.05 to 0.08, the addition beingmade to a paper pulp slurry'prior to the laying of a wet paper mat.

References Cited UNITED STATES PATENTS 3,414,530 12/1968 Zilkha et a1.,260 233.3 R

US. Cl. X.R.

